With increase in amount of data used and accumulated in a computer system, storage capacity of a storage unit included in the computer system increases. In order to save the cost of instruction, maintenance and management cost of the storage unit having larger capacity, the storage unit has been centralized by utilizing a SAN (Storage Area Network) which is an exclusive network for storage. Moreover, various techniques for the SAN have been introduced (for example, refer to Marc Farley, “Building Storage Networks, Second Edition”, Osborne/McGraw-Hill, 2001, pp. 86–90, pp. 515–516.).
Marc Farley's reference describes, in its pages 86 to 90, the technique referred to as “virtualization”. With this technique, virtual storage units are created in place of a physical storage unit to store data and provided to the computer and application programs to be executed by this computer. In this reference, it is also described that virtualization may be realized in many layers and the virtualization consists of several functions such as a function to summarize a plurality of physical storage units into a virtual memory region and a function to divide a physical storage unit into a plurality of virtual storage regions.
This Marc Farley's reference also describes, in its pages 515 to 516, the technique to employ an access model which is different from that in the prior art and which is referred to as the “Object-Based Storage(OBS)”. With the hard disk drive of the prior art, a computer calculates a logical block address and designates a memory region for access using such calculated logical block address. Meanwhile, in the OBS, an access destination (address) is designated using storage location information required for calculation of memory region of storage unit in which data is stored. Accordingly, calculation cost of logical block address in computers can be saved.
As another design goal of OBS, realization of storage unit holding the self-management function may be listed. The OBS realizes the storage unit with the data management function for the local region of storage unit by utilizing file system attribute or the like. As an example of this data management function, error correction, memory region management, backup, mirror and data migration may be listed.
When application software to be executed on the computer system using a SAN is considered, many application softwares use the data stored in a database (DB) as the basic data and therefore a database management system (DBMS) which is software to perform a series of processes and management in regard to DB is extremely important.
Here, a function to facilitate management of data storage region in the DBMS is known (for example, refer to “Oracle9i Database Administrator's Guide Release 1 (9.0.1)”, Oracle, Part No. A90117-01, 2001, Chapter 3 Using Oracle-Managed Files.). The Oracle's Guide describes the automatic management function of data storage region referred to as Oracle-Managed Files (OMF). In the OMF, it is assumed that data is stored in a data file created by utilizing the standard file system interface. When a storage region is newly required for every predetermined external storage region management structure (such as tablespace) the data file storing data is automatically expanded and a new data file is generated. Moreover, the data files which are no longer required are deleted adequately.